A photolithographic technique for fabricating micro-order or submicron-order fine patterns within an electronic device, such as a semiconductor, has been at the core of micromachining techniques for mass production. A demand for an increase in integration and an increase in density of semiconductor devices in recent years has led to many improvements in micromachining techniques. In particular, as the minimum possible machining dimension approaches the exposure wavelength, photolithographic techniques using light sources for shorter wavelengths ranging from g-line (436 nm) and i-line (365 nm) in a high pressure mercury lamp to a KrF excimer laser (248 nm), have been developed. A change in exposure wavelength has led to the development of photoresists made from materials suitable for the wavelength being used. In any of the photoresists suitable for the above wavelengths, aqueous alkali development utilizing the solubility of resins having a phenol structure or polymeric materials in an aqueous alkali has been adopted on a commercial scale, although they are different from each other in photoactive compound and photoactivating mechanism. These resins and polymeric materials necessarily contain many aromatic rings which are also chemical structural elements for enhancing the etching resistance in the step of dry etching after the formation of the resist pattern.
Negative resists prepared from resins having the above-mentioned phenol structure are classified into ones of a crosslinking type as disclosed in Japanese Patent Laid-Open No. 164045/1987 and ones of a dissolution inhibition type as disclosed in Japanese Patent Laid-Open No. 165359/1992. In any type, submicron-order fine patterns can be formed without causing swelling.
Photolithography using an ArF excimer laser (193 nm) as a light source has become more and more commonplace for photolithography which can provide a minimum possible machining dimension of less than 0.25 μm. This wavelength corresponds to the absorption maximum of an aromatic ring. Therefore, in the photoresist material composed mainly of a phenol structure, which has been used on a commercial scale, the formation of a latent image in response to the exposure is limited to a portion which is very near the surface of the photoresist film, making it difficult to form a fine resist pattern by aqueous alkali development.
On the other hand, various resist materials have been proposed which have high transmittances in the above-mentioned wavelength region while possessing high dry-etching resistance. Utilization of an adamantane structure (Japanese Patent Laid-Open Nos. 39665/1992 and 265212/1993) and utilization of a norbornane structure (Japanese Patent Laid-Open Nos. 80515/1993 and 257284/1993) have been proposed as chemical structures which are transparent in the far ultraviolet region including the wavelength 193 nm of the ArF excimer laser and, instead of the aromatic ring, can impart dry-etching resistance to the resist material. Japanese Patent Laid-Open Nos. 28237/1995 and 259626/1996 disclose that, in addition to these structures, general alicyclic structures, such as a tricyclodecanyl group, are also useful.
Regarding resist materials which have been rendered developable with an aqueous alkali by using a polymer having a chemical structure transparent in the far ultraviolet region including the wavelength 193 nm of the ArF excimer laser and, utilization of the carboxylic acid structure of acrylic acid or methacrylic acid, has been attempted in Japanese Patent Laid-Open Nos. 39665/1992, 184345/1992, 226461/1992, and 80515/1993. In these publications, the aqueous alkali solubility of a portion dissolved in a developing solution in the aqueous alkali development depends upon the carboxylic acid structure of acrylic acid or methacrylic acid. Furthermore, Japanese Patent Laid-Open No. 8-259626 discloses a polymeric compound in which a carboxylic acid group has been provided in an alicyclic structure introduced into the side chain of a methacrylic acid ester.